It's 40 degrees in Winter and up to 50 degrees in Summer. The reason being that after stoking, there is a large mass of red hot coal in the pot and that creates enough heat to raise the boiler another 30 degrees easily, after the stoker has shut down. With low demand for domestic or heating water, there is nothing to draw down the boiler water temperature and it can sit there for hours and not lose much heat.
Add to that, if your high limit is 190 and the temperature drops to 185 and the timer kicks in its half hour cycle (below the high limit), you could easily jump to well over 200 degrees. So, it's an experimental experience to get all the aquastats set properly so the fire doesn't go out.
In the efm boiler, with the nightly setback of 10 degrees, the cold water returning to the boiler in the morning can draw down the boiler temperature to 120 and affect the outfire control which will shut down the stoker until it's manually reset. On the other end, the second high limit aquastat, which must also be manually reset, can be affected if the operating aquastat high limit is set too high. The second aquastat is 240 degrees maximum. Both of these shutdowns have ocurred. And finally, the operating aquastat must have a 40 degree range, so you see all the stuff that must be worked out with the extra aquastats.